Onto a recordable or rewritable optical disc such as a DVD-R (DVD-Recordable) or a DVD-RW (DVD-Rerecordable), information is recorded thereon by irradiating a laser light on its recording surface. At the areas on the recording surface of the optical disc where the laser light is irradiated, the property of the optical recording medium forming the optical disc is physically changed because of the increased temperature. This produces recording marks on the recording surface.
Namely, the laser light is modulated by recording pulses having time widths corresponding to information to be recorded, so that the laser pulses having lengths corresponding to information to be recorded are generated and irradiated on the optical disc. Thus, recording marks having lengths corresponding to the information to be recorded can be formed on the optical disc.
One approach recently used is to form a recording mark by a pulse train having a plurality of short pulses, rather than by a single laser pulse. This approach, called “write strategy”, introduces less heat accumulation on the recording surface of the optical disc compared to the approach irradiating a single recording laser pulse. Therefore, uniform temperature distribution can be achieved on the recording surface on which the recording marks are formed. This can prevent undesired tear drop-shaped recording marks from being formed, and enables the formation of the recording marks of preferred shape.
In the case of DVD-R, for example, the recording pulse train consists of a plurality of pulses which magnitudes varying between a certain bias power level and write power level. That is, based on recording data, the areas on the recording surface of the optical disc where no recording marks are to be formed (referred to as “space periods” hereafter) are irradiated with the laser light of the bias power. The areas on the recording surface of the optical disc where recording marks are to be formed (referred to as “mark periods” hereafter) are irradiated with the laser light of the power corresponding to the recording pulse train having magnitudes varying between the bias power and the write power. Consequently, the recording marks are formed on the recording surface.
Though the bias power level in the recording pulse is prescribed by a DVD-R standard and the like, the bias power level different from a prescribed value may be used in a drive apparatus of the optical disc. For example, at the time of recording the information, during the period in which no recording mark is formed, a gain control of a recording laser power and various kinds of servo controls are executed by using the bias power level. Therefore, it can be thought that the bias power level is set to be higher than the prescribed value in order to stabilize the control of the laser power and the servo control. On the contrary, it is preferable that the bias power level is low in terms of improving the recording characteristic of the information by the recording pulse. Therefore, it can be thought that the bias power level is set to be lower than the prescribed value.
However, when the bias power level is varied, there is such a problem that the optimum recording characteristic cannot problematically be obtained even if the recording is performed by the write strategy designated in advance.